Lubricant composition for hydraulic oil

ABSTRACT

The present invention relates to a lubricant composition, and more particularly to a lubricant composition, which has superior oxidation stability and friction characteristics even under harsh conditions of high temperature and high pressure and is thus suitable for use in hydraulic oil. The lubricant composition of the present invention includes a base oil, a liquid olefin copolymer, a phosphorothioate compound, and phosphonium phosphate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority from Korean Patent Application No. 10-2019-0023681, filed on Feb. 28, 2019 with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION 1. Technical Field

The present invention relates to a lubricant composition, and more particularly to a lubricant composition, which has superior oxidation stability and friction characteristics even under harsh conditions of high temperature and high pressure and is thus suitable for use in hydraulic oil.

2. Description of the Related Art

A lubricant is an oily material used to reduce the generation of frictional force on the friction surface of a machine or to dissipate frictional heat generated from the friction surface. Because of the wide variety of machinery that requires lubrication and the wide variety of conditions under which such machinery works, lubricants vary in type and quality. Depending on the application thereof, different types of base oil must be used. In particular, when a lubricant is used for an airplane or an advanced hydraulic system, hydraulic oil having a strong flame-retarding effect is required.

Any type of hydraulic oil used in industrial fields is a medium of power transmission and plays roles in lubrication, rust prevention, sealing and cooling of respective parts of hydraulic equipment. The hydraulic oil is manufactured by adding additives to base oil, and is largely classified into mineral hydraulic oil (petroleum-based hydraulic oil) and synthetic hydraulic oil depending on the type of base oil, synthetic hydraulic oil being classified into polyalphaolefin-based hydraulic oil and ester-based hydraulic oil.

Meanwhile, the operating temperature range of hydraulic oil varies, and especially in the summer, may be 75 to 850 or higher. At such temperatures, however, mineral hydraulic oil and polyalphaolefin-based hydraulic oil generate a lot of oil vapor. The occurrence of such oil vapor causes a problem of increasing the evaporation loss of hydraulic oil, and also promotes the oxidation of hydraulic oil. Hence, it is necessary to minimize the generation of oil vapor. In particular, mineral hydraulic oil, which accounts for most hydraulic oil, requires additional measures to improve oxidation stability due to the characteristics of the base feedstock oil. Moreover, since hydraulic systems are recently becoming more and more sophisticated, hydraulic oil is required to have superior friction characteristics.

Therefore, the present inventors have developed a lubricant composition for hydraulic oil, which has superior thermal and oxidation stability and is capable of reducing mechanical wear of hydraulic equipment.

CITATION LIST Patent Literature

(Patent Document 0001) Korean Patent No. 10-0201759

(Patent Document 0002) Korean Patent Application Publication No. 10-2008-0109015

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the problems encountered in the related art, and an objective of the present invention is to provide a lubricant composition, in which a functional additive for friction reduction and an ethylene-alphaolefin liquid random copolymer having a high viscosity index are mixed, thereby exhibiting superior friction characteristics, thermal stability and oxidation stability.

Another objective of the present invention is to provide a lubricant composition for hydraulic oil, which is capable of reducing the mechanical wear of hydraulic equipment and energy consumption when applied to hydraulic equipment and of decreasing evaporation loss due to low changes in the physical properties of hydraulic oil, and thus may be used for a long period of time.

In order to accomplish the above objectives, the present invention provides a lubricant composition, comprising a base oil, a liquid olefin copolymer, a phosphorothioate compound, and phosphonium phosphate.

The base oil may be at least one selected from the group consisting of mineral oil, polyalphaolefin (PAO) and ester.

The liquid olefin copolymer may be prepared by copolymerizing ethylene and alphaolefin in the presence of a single-site catalyst system, and the single-site catalyst system preferably includes a metallocene catalyst, an organometallic compound and an ionic compound.

The liquid olefin copolymer may have a coefficient of thermal expansion of 3.0 to 4.0.

The liquid olefin copolymer may be included in an amount of 0.5 to 30 wt %, and preferably 0.5 to 25 wt %, in the lubricant composition of the present invention.

The phosphorothioate compound may be included in an amount of 0.1 to 5.0 wt %, and preferably 0.1 to 3.0 wt %, in the lubricant composition.

The phosphonium phosphate may be included in an amount of 0.05 to 3.0 wt %, and preferably 0.1 to 1.5 wt %, in the lubricant composition.

The lubricant composition may have an SRV friction coefficient of 0.1 to 0.35 and a traction coefficient of 0.15 to 0.3.

According to the present invention, a lubricant composition includes phosphorothioate, phosphonium phosphate, and an ethylene-alphaolefin liquid random copolymer having a high viscosity index, which are mixed together, thereby improving friction characteristics and thermal and oxidation stability, and is capable of reducing the mechanical wear of hydraulic equipment and energy consumption when applied to hydraulic equipment, thereby maximizing energy-saving effects.

Also, according to the present invention, the lubricant composition has low changes in the physical properties of hydraulic oil, thus decreasing evaporation loss, and can endure 1000 min or more, and preferably 1200 min or more, in an RBOT oxidation stability test (ASTM D2271), thereby enabling the long-term use thereof as hydraulic oil.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, a detailed description will be given of the present invention.

The present invention relates to a lubricant composition, which has superior oxidation stability and friction characteristics and is thus suitable for use in hydraulic oil. Hence, the lubricant composition of the present invention includes a base oil, a liquid olefin copolymer, a phosphorothioate compound, and phosphonium phosphate.

Here, the base oil varies from the aspects of viscosity, heat resistance, oxidation stability and the like depending on the manufacturing method or refining method, but is generally classified into mineral oil and synthetic oil. The API (American Petroleum Institute) classifies base oil into five types, namely Group I, II, III, IV and V. These types, based on API ranges, are defined in API Publication 1509, 15^(th) Edition, Appendix E, April 2002, and are shown in Table 1 below.

TABLE 1 Saturated hydrocarbon (%) Sulfur (%) Viscosity index Group I <90 >0.03 80 ≤ VI < 120 Group II ≥90 ≤0.03 80 ≤ VI < 120 Group III ≥90 ≤0.03 VI ≥ 120 Group IV PAO (Poly Alpha Olefin) Group V Ester & Others

In the lubricant composition of the present invention, the base oil may be at least one selected from the group consisting of mineral oil, polyalphaolefin (PAO) and ester, and may be any type among Groups I to V based on the API ranges.

More specifically, mineral oil belongs to Groups I to III based on the API ranges, and mineral oil may include oil resulting from subjecting a lubricant distillate fraction, obtained through atmospheric distillation and/or vacuum distillation of crude oil, to at least one refining process of solvent deasphalting, solvent extraction, hydrogenolysis, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid cleaning, and white clay treatment; wax isomerized mineral oil; or a gas-to-liquid (GLT) oil obtained via the Fischer-Tropsch process.

The synthetic oil belongs to Group IV or V based on the API ranges, and polyalphaolefin belonging to Group IV may be obtained through oligomerization of a higher alphaolefin using an acid catalyst, as disclosed in U.S. Pat. Nos. 3,780,128, 4,032,591, Japanese Patent Application Publication No. Hei. 1-163136, and the like, but the present invention is not limited thereto.

Examples of the synthetic oil belonging to Group V include alkyl benzenes, alkyl naphthalenes, isobutene oligomers or hydrides thereof, paraffins, polyoxy alkylene glycol, dialkyl diphenyl ether, polyphenyl ether, ester, and the like.

Here, the alkyl benzenes and alkyl naphthalenes are usually dialkylbenzene or dialkylnaphthalene having an alkyl chain length of 6 to 14 carbon atoms, and the alkyl benzenes or alkyl naphthalenes are prepared through Friedel-Crafts alkylation of benzene or naphthalene with olefin. The alkylated olefin used in the preparation of alkyl benzenes or alkyl naphthalenes may be linear or branched olefins or combinations thereof.

Also, examples of the ester include, but are not limited to, ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, tridecyl pelargonate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, trimethylolpropane caprylate, trimethylolpropane pelargonate, trimethylolpropane triheptanoate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, pentaerythritol tetraheptanoate, and the like.

In the lubricant composition of the present invention, the liquid olefin copolymer is prepared by copolymerizing ethylene and alphaolefin monomers in the presence of a single-site catalyst system in order to uniformly distribute alphaolefin units in the copolymer chain. Preferably, the liquid olefin copolymer is prepared by reacting ethylene and alphaolefin monomers in the presence of a single-site catalyst system including a crosslinked metallocene compound, an organometallic compound, and an ionic compound for forming an ion pair through reaction with the crosslinked metallocene compound.

Here, the metallocene compound included in the single-site catalyst system may be at least one selected from the group consisting of Chemical Formulas 1 to 6 below.

In Chemical Formulas 1 to 4,

M is a transition metal selected from the group consisting of titanium, zirconium, and hafnium,

B is absent or is a linking group including a C1-C20 alkylene group, a C6-C20 arylene group, C1-C20 dialkyl silicon, C1-C20 dialkyl germanium, a C1-C20 alkylphosphine group or a C1-C20 alkylamine group,

X₁ and X₂, which are the same as or different from each other, are each independently a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C7-C40 alkylaryl group, a C7-C40 arylalkyl group, a C1-C20 alkylamido group, a C6-C20 arylamido group, a C1-C20 alkylidene group or a C1-C20 alkoxy group, and

R₁ to R₁₀, which are the same as or different from each other, are each independently hydrogen, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C6-C20 aryl group, a C7-C20 alkylaryl group, a C7-C20 arylalkyl group, a C5-C60 cycloalkyl group, a C4-C20 heterocyclic group, a C1-C20 alkynyl group, a C6-C20-aryl-containing hetero group or a silyl group.

In Chemical Formulas 5 and 6,

M is a transition metal selected from the group consisting of titanium, zirconium, and hafnium,

B is absent or is a linking group including a C1-C20 alkylene group, a C6-C20 arylene group, a C1-C20 dialkyl silicon, a C1-C20 dialkyl germanium, a C1-C20 alkylphosphine group or a C1-C20 alkylamine group,

X₁ and X₂, which are the same as or different from each other, are each independently a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C7-C40 alkylaryl group, a C7-C40 arylalkyl group, a C1-C20 alkylamido group, a C6-C20 arylamido group, a C1-C20 alkylidene group or a C1-C20 alkoxy group, and

R₁ to R₁₀, which are the same as or different from each other, are each independently hydrogen, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C6-C20 aryl group, a C7-C20 alkylaryl group, a C7-C20 arylalkyl group, a C5-C60 cycloalkyl group, a C4-C20 heterocyclic group, a C1-C20 alkynyl group, a C6-C20-aryl-containing hetero group or a silyl group.

Furthermore, all of R₁₁, R₁₃ and R₁₄ are hydrogen, and each of R₁₂ radicals, which are the same as or different from each other, may independently be hydrogen, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C6-C20 aryl group, a C7-C20 alkylaryl group, a C7-C20 arylalkyl group, a C5-C60 cycloalkyl group, a C4-C20 heterocyclic group, a C1-C20 alkynyl group, a C6-C20-aryl-containing hetero group or a silyl group.

Also, the metallocene compound of Chemical Formulas 2 to 6 may include a compound substituted through a hydroaddition reaction, and a preferred example thereof includes dimethylsilyl bis(tetrahydroindenyl) zirconium dichloride.

The organometallic compound included in the single-site catalyst system may be at least one selected from the group consisting of an organoaluminum compound, an organomagnesium compound, an organozinc compound and an organolithium compound, and is preferably an organoaluminum compound. The organoaluminum compound may be at least one selected from the group consisting of, for example, trimethylaluminum, triethylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, dimethylchloroaluminum, dimethylisobutylaluminum, dimethylethylaluminum, diethylchloroaluminum, triisopropylaluminum, triisobutylaluminum, tricyclopentylaluminum, tripentylaluminum, triisopentylaluminum, ethyldimethylaluminum, methyldiethylaluminum, triphenylaluminum, methylaluminoxane, ethylaluminoxane, isobutylaluminoxane and butylaluminoxane, and is preferably triisobutylaluminum.

The ionic compound included in the single-site catalyst system may be at least one selected from the group consisting of organoboron compounds such as dimethylanilinium tetrakis(perfluorophenyl)borate, triphenylcarbenium tetrakis(perfluorophenyl)borate, and the like.

The component ratio of the single-site catalyst system may be determined in consideration of catalytic activity, and the molar ratio of metallocene catalyst:ionic compound:organometallic compound is preferably adjusted in the range of 1:1:5 to 1:10:1000 in order to ensure desired catalytic activity.

Furthermore, the components of the single-site catalyst system may be added at the same time or in any sequence to an appropriate solvent and may thus function as an active catalyst system. Here, the solvent may include, but is not limited to, a hydrocarbon solvent such as pentane, hexane, heptane, etc., or an aromatic solvent such as benzene, toluene, xylene, etc., and any solvent usable in the preparation may be used.

Also, the alphaolefin monomer used in the preparation of the liquid olefin copolymer includes a C2-C20 aliphatic olefin, and may specifically be at least one selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-decene, 1-dodecene and 1-tetradecene, and may include isomeric forms, but the present invention is not limited thereto. In the copolymerization, the monomer content is 1 to 95 mol %, preferably 5 to 90 mol %.

The liquid olefin copolymer required in the present invention has a coefficient of thermal expansion of 3.0 to 4.0 and a bromine number of 0.1 or less.

The liquid olefin copolymer may be included in an amount of 0.5 to 30 wt %, and preferably 0.5 to 25 wt %, based on 100 wt % of the lubricant composition. If the amount of the liquid olefin copolymer is less than 0.5 wt % based on 100 wt % of the lubricant composition, stability may deteriorate. On the other hand, if the amount thereof exceeds 30 wt %, application of the resulting composition to hydraulic oil becomes difficult, which is undesirable.

The phosphorothioate compound, serving as a friction-reducing agent, may be at least one selected from the group consisting of monophosphorothioate, diphosphorothioate, triphosphorothioate, methylphosphorothioate, ethylphosphorothioate and sulfonylphosphorothioate. When the phosphorothioate compound is included in the lubricant composition, it may exhibit synergistic effects with an existing wear-resistant agent and friction reduction effects, and additionally, energy-saving effects may be achieved through friction reduction.

The phosphorothioate compound may be included in an amount of 0.1 to 5.0 wt %, and preferably 0.1 to 3.0 wt %, based on 100 wt % of the lubricant composition. If the amount of the phosphorothioate compound is less than 0.1 wt % based on 100 wt % of the lubricant composition, the friction reduction effect is insignificant. On the other hand, if the amount thereof exceeds 5.0 wt %, the additional reduction effect is insignificant despite the excessive addition thereof, which is undesirable.

The phosphonium phosphate is a material having the structure of Chemical Formula 7 below, and is used as a friction/wear-reducing agent. In particular, when it is used together with the phosphorothioate compound, the effects thereof may be maximized.

The phosphonium phosphate exists in the form of an ionic liquid having both a phosphonium anion and a phosphate cation, and, among various phosphonium compounds, exhibits a characteristic friction/wear reduction effect.

Also, the phosphonium phosphate may be included in an amount of 0.05 to 3.0 wt %, and preferably 0.1 to 1.5 wt %, based on 100 wt % of the lubricant composition. If the amount of the phosphonium phosphate is less than 0.05 wt % based on 100 wt % of the lubricant composition, the friction/wear reduction effect may be insignificant. On the other hand, if the amount thereof exceeds 3.0 wt %, there is no synergistic effect thereof with the phosphorothioate compound, and wear may increase, which is undesirable.

The lubricant composition of the present invention may further include an additive selected from the group consisting of an antioxidant, a metal cleaner, an anticorrosive agent, a foam inhibitor, a pour-point depressant, a viscosity modifier, a wear-resistant agent and combinations thereof.

The antioxidant may be included in an amount of 0.01 to 5.0 wt % based on 100 wt % of the lubricant composition, and is preferably used in the form of a mixture of a phenolic antioxidant and an aminic antioxidant, more preferably a mixture of 0.01 to 3.0 wt % of the phenolic antioxidant and 0.01 to 3.0 wt % of the aminic antioxidant.

The phenolic antioxidant may be any one selected from the group consisting of 2,6-dibutylphenol, hindered bisphenol, high-molecular-weight hindered phenol, and hindered phenol with thioether.

The aminic antioxidant may be any one selected from the group consisting of diphenylamine, alkylated diphenylamine and naphthylamine, and preferably, the alkylated diphenylamine is dioctyldiphenylamine, octylated diphenylamine, or butylated diphenylamine.

The metal cleaner may be at least one selected from the group consisting of metallic phenate, metallic sulfonate, and metallic salicylate, and preferably, the metal cleaner is included in an amount of 0.1 to 10.0 wt % based on 100 wt % of the lubricant composition.

The anticorrosive agent may be a benzotriazole derivative, and is preferably any one selected from the group consisting of benzotriazole, 2-methylbenzotriazole, 2-phenylbenzotriazole, 2-ethylbenzotriazole and 2-propylbenzotriazole. The anticorrosive agent may be included in an amount of 0 to 4.0 wt % based on 100 wt % of the lubricant composition.

The foam inhibitor may be polyoxyalkylene polyol, and preferably, the foam inhibitor is included in an amount of 0 to 4.0 wt % based on 100 wt % of the lubricant composition.

The pour-point depressant may be poly(methacrylate), and preferably, the pour-point depressant is included in an amount of 0.01 to 5.0 wt % based on 100 wt % of the lubricant composition.

The viscosity modifier may be polyisobutylene or polymethacrylate, and preferably, the viscosity modifier is included in an amount of 0 to 15 wt % based on 100 wt % of the lubricant composition.

The wear-resistant agent may be at least one selected from the group consisting of organic borates, organic phosphites, organic sulfur-containing compounds, zinc dialkyl dithiophosphate, zinc diaryl dithiophosphate and phosphosulfurized hydrocarbon, and preferably, the wear-resistant agent is included in an amount of 0.01 to 3.0 wt %.

The lubricant composition of the present invention has an SRV friction coefficient of 0.1 to 0.35. Moreover, the lubricant composition has a traction coefficient of 0.15 to 0.3.

A better understanding of the present invention through the following examples. However, the present invention is not limited to these examples, but may be embodied in other forms. These examples are provided to thoroughly explain the invention and to sufficiently transfer the spirit of the present invention to those skilled in the art.

1. Preparation of Additive Composition

An additive composition for use in the lubricant composition of the present invention was prepared as shown in Table 2 below.

TABLE 2 Composi- Composi- Additive composition tion A tion B Antioxidant 2,6-dibutylphenol 1 1.5 Diphenylamine 0.8 1 Metal cleaner Metallic phenate 0.2 0.6 Anticorrosive Benzotriazole 0.3 1.0 agent Foam inhibitor Polyoxyalkylene polyol 0.01 0.02 Pour-point Polymethacrylate 0.2 0.5 depressant Viscosity Polyisobutylene — 1.0 modifier Wear-resistant Zinc dialkyl dithiophosphate 0.2 1.1 agent

2. Preparation of Liquid Olefin Copolymer

A liquid olefin copolymer was prepared using an oligomerization method through a catalytic reaction process. Depending on the reaction time and conditions, which follow, liquid olefin copolymers having different molecular weights were prepared, and the properties thereof are shown in Table 3 below.

The reaction time and conditions were increased by 4 hr each from 20 hr. Here, the amounts of hydrogen and comonomer C3, which were added thereto, were increased by 10% each, and polymerization was performed under individual conditions, and the resulting polymers were classified depending on the molecular weight thereof.

TABLE 3 Main properties Alphaolefin Evaporation Thickening Power (10 CoE of Thermal copolymer Loss (%) wt % in 150N) Expansion Copolymer I 1.28 6 3.00 to 3.20 Copolymer II 0.54 7 3.20 to 3.40 Copolymer III 0.10 8 3.40 to 3.50 Copolymer IV 0.001 10 3.50 to 3.60 Copolymer V 0.0001 12 3.60 to 3.70 Copolymer VI 0.00001 14 3.70 to 3.80

3. Preparation of Lubricant Composition for Hydraulic Oil

A lubricant composition was prepared by mixing a base oil, the liquid olefin copolymer, a phosphorothioate compound, phosphonium phosphate and the additive prepared above, as shown in Tables 4 and 5 below. Here, the base oil was polyalphaolefin (PAO 4 cSt, available from Chevron Philips) having kinematic viscosity of 4 cSt at 1000, and the phosphorothioate compound was monophosphorothioate.

Preparation Examples 1 to 67 and Comparative Examples 1 to 14. Lubricant Composition for Hydraulic Oil Including Additive A

TABLE 4 Phosphorothioate Alphaolefin Compound Phosphonium Composition Base oil copolymer Monophosphorothioate phosphate Additive A Preparation 97.135 Copolymer 0.1 0.005 2.71 Example 1 I 0.05 Preparation 96.735 Copolymer 0.5 0.005 2.71 Example 2 I 0.05 Preparation 95.74 Copolymer 1.0 0.5 2.71 Example 3 I 0.05 Preparation 93.74 Copolymer 3.0 0.5 2.71 Example 4 I 0.05 Preparation 88.74 Copolymer 5.0 3.5 2.71 Example 5 I 0.05 Preparation 96.64 Copolymer 0.1 0.05 2.71 Example 6 I 0.5 Preparation 95.74 Copolymer 1.0 0.05 2.71 Example 7 I 0.5 Preparation 93.69 Copolymer 3.0 0.1 2.71 Example 8 I 0.5 Preparation 92.09 Copolymer 0.1 0.1 2.71 Example 9 I 5 Preparation 91.69 Copolymer 0.5 0.1 2.71 Example 10 I 5 Preparation 89.19 Copolymer 3.0 0.1 2.71 Example 11 I 5 Preparation 38.29 Copolymer 5.0 4.0 2.71 Example 12 I 5 Preparation 86.89 Copolymer 0.1 0.3 2.71 Example 13 I 10 Preparation 86.49 Copolymer 0.5 0.3 2.71 Example 14 I 10 Preparation 85.99 Copolymer 1.0 0.3 2.71 Example 15 I 10 Preparation 78.79 Copolymer 5.0 3.5 2.71 Example 16 I 10 Preparation 76.69 Copolymer 0.1 0.5 2.71 Example 17 I 20 Preparation 76.29 Copolymer 0.5 0.5 2.71 Example 18 I 20 Preparation 70.29 Copolymer 5.0 2.0 2.71 Example 19 I 20 Preparation 66.29 Copolymer 0.5 0.5 2.71 Example 20 I 30 Preparation 60.79 Copolymer 5.0 1.5 2.71 Example 21 I 30 Preparation 60.79 Copolymer 0.5 1.0 2.71 Example 22 I 35 Preparation 61.19 Copolymer 1.0 0.1 2.71 Example 23 I 35 Preparation 56.79 Copolymer 3.0 2.5 2.71 Example 24 I 35 Preparation 53.79 Copolymer 5.0 3.5 2.71 Example 25 I 35 Preparation 47.29 Copolymer 10.0  5.0 2.71 Example 26 I 35 Preparation 47.235 Copolymer  0.05 0.005 2.71 Example 27 I 50 Preparation 46.285 Copolymer 1.0 0.005 2.71 Example 28 I 50 Preparation 38.79 Copolymer 5.0 3.5 2.71 Example 29 I 50 Preparation 96.64 Copolymer 0.1 0.5 2.71 Example 30 II 0.05 Preparation 95.24 Copolymer 0.5 1.5 2.71 Example 31 II 0.05 Preparation 94.24 Copolymer 1.0 2.0 2.71 Example 32 II 0.05 Preparation 92.24 Copolymer 3.0 2.0 2.71 Example 33 II 0.05 Preparation 90.24 Copolymer 5.0 2.0 2.71 Example 34 II 0.05 Preparation 96.19 Copolymer 0.1 0.5 2.71 Example 35 II 0.5 Preparation 93.29 Copolymer 3.0 0.5 2.71 Example 36 II 0.5 Preparation 83.79 Copolymer 5.0 3.5 2.71 Example 37 II 5 Preparation 78.79 Copolymer 5.0 3.5 2.71 Example 38 II 10 Preparation 72.285 Copolymer 5.0 0.005 2.71 Example 39 II 20 Preparation 97.139 Copolymer 0.1 0.001 2.71 Example 40 III 0.05 Preparation 95.24 Copolymer 0.5 1.5 2.71 Example 41 III 0.05 Preparation 94.24 Copolymer 1.0 2.0 2.71 Example 42 III 0.05 Preparation 92.24 Copolymer 3.0 2.0 2.71 Example 43 III 0.05 Preparation 91.69 Copolymer 0.1 0.5 2.71 Example 44 III 5 Preparation 91.29 Copolymer 0.5 0.5 2.71 Example 45 III 5 Preparation 76.29 Copolymer 0.5 0.5 2.71 Example 46 III 20 Preparation 75.29 Copolymer 1.0 1.0 2.71 Example 47 III 20 Preparation 91.19 Copolymer 0.1 1.0 2.71 Example 48 IV 5 Preparation 88.29 Copolymer 3.0 1.0 2.71 Example 49 IV 5 Preparation 76.69 Copolymer 0.5 0.1 2.71 Example 50 IV 20 Preparation 73.29 Copolymer 3.0 1.0 2.71 Example 51 IV 20 Preparation 92.09 Copolymer 0.1 0.1 2.71 Example 52 V 5 Preparation 91.69 Copolymer 0.5 0.1 2.71 Example 53 V 5 Preparation 78.79 Copolymer 5.0 3.5 2.71 Example 54 V 10 Preparation 77.14 Copolymer 0.1 0.05 2.71 Example 55 V 20 Preparation 76.69 Copolymer 0.5 0.1 2.71 Example 56 V 20 Preparation 68.79 Copolymer 5.0 3.5 2.71 Example 57 V 20 Preparation 45.79 Copolymer 1.0 0.5 2.71 Example 58 V 50 Preparation 43.79 Copolymer 3.0 0.5 2.71 Example 59 V 50 Preparation 42.289 Copolymer 5.0 0.001 2.71 Example 60 V 50 Preparation 93.64 Copolymer 0.1 3.5 2.71 Example 61 VI 0.05 Preparation 93.24 Copolymer 0.5 3.5 2.71 Example 62 VI 0.05 Preparation 92.74 Copolymer 1.0 3.5 2.71 Example 63 VI 0.05 Preparation 92.14 Copolymer 0.1 0.05 2.71 Example 64 VI 5 Preparation 91.69 Copolymer 0.5 0.1 2.71 Example 65 VI 5 Preparation 77.09 Copolymer 0.1 0.1 2.71 Example 66 VI 20 Preparation 76.29 Copolymer 0.5 0.5 2.71 Example 67 VI 20 Comparative 97.24 Copolymer — — 2.71 Example 1 I 0.05 Comparative 93.74 Copolymer — 3.5 2.71 Example 2 II 0.05 Comparative 87.29 Copolymer — — 2.71 Example 3 II 10 Comparative 73.29 Copolymer — 4.0 2.71 Example 4 II 20 Comparative 67.29 Copolymer — — 2.71 Example 5 II 30 Comparative 87.29 Copolymer 5.0 — 2.71 Example 6 III 5 Comparative 82.29 Copolymer 5.0 — 2.71 Example 7 III 10 Comparative 72.29 Copolymer 5.0 — 2.71 Example 8 III 20 Comparative 88.79 Copolymer — 3.5 2.71 Example 9 IV 5 Comparative 87.29 Copolymer 5.0 — 2.71 Example 10 IV 5 Comparative 82.29 Copolymer 10.0  — 2.71 Example 11 IV 5 Comparative 63.79 Copolymer — 3.5 2.71 Example 12 V 30 Comparative 58.79 Copolymer — 3.5 2.71 Example 13 V 35 Comparative 93.74 Copolymer — 3.5 2.71 Example 14 VI 0.05

Preparation Examples 68 to 116 and Comparative Examples 15 to 53. Lubricant Composition for Hydraulic Oil Including Additive B

TABLE 5 Phosphorothioate Alphaolefin compound Phosphonium Composition Base oil copolymer Monophosphorothioate phosphate Additive B Preparation 92.58 Copolymer 0.1 0.1 6.72 Example 68 I 0.5 Preparation 92.18 Copolymer 0.5 0.1 6.72 Example 69 I 0.5 Preparation 91.68 Copolymer 1.0 0.1 6.72 Example 70 I 0.5 Preparation 88.08 Copolymer 0.1 0.1 6.72 Example 71 I 5 Preparation 87.28 Copolymer 0.5 0.5 6.72 Example 72 I 5 Preparation 86.78 Copolymer 1.0 0.5 6.72 Example 73 I 5 Preparation 82.68 Copolymer 0.1 0.5 6.72 Example 74 I 10 Preparation 81.78 Copolymer 1.0 0.5 6.72 Example 75 I 10 Preparation 79.78 Copolymer 3.0 0.5 6.72 Example 76 I 10 Preparation 73.08 Copolymer 0.1 0.1 6.72 Example 77 I 20 Preparation 72.28 Copolymer 0.5 0.5 6.72 Example 78 I 20 Preparation 71.78 Copolymer 1.0 0.5 6.72 Example 79 I 20 Preparation 92.18 Copolymer 0.1 0.5 6.72 Example 80 II 0.5 Preparation 88.78 Copolymer 3.0 1.0 6.72 Example 81 II 0.5 Preparation 54.78 Copolymer 5.0 3.5 6.72 Example 82 II 30 Preparation 93.08 Copolymer 0.1  0.05 6.72 Example 83 III 0.05 Preparation 91.73 Copolymer 0.5 1.0 6.72 Example 84 III 0.05 Preparation 91.23 Copolymer 1.0 1.0 6.72 Example 85 III 0.05 Preparation 89.23 Copolymer 3.0 1.0 6.72 Example 86 III 0.05 Preparation 86.68 Copolymer 0.1 1.5 6.72 Example 87 III 5 Preparation 86.28 Copolymer 0.5 1.5 6.72 Example 88 III 5 Preparation 79.78 Copolymer 5.0 3.5 6.72 Example 89 III 5 Preparation 74.78 Copolymer 5.0 3.5 6.72 Example 90 III 10 Preparation 71.28 Copolymer 0.5 1.5 6.72 Example 91 III 20 Preparation 70.78 Copolymer 1.0 1.5 6.72 Example 92 III 20 Preparation 34.78 Copolymer 5.0 3.5 6.72 Example 93 III 50 Preparation 89.63 Copolymer 0.1 3.5 6.72 Example 94 IV 0.05 Preparation 89.23 Copolymer 0.5 3.5 6.72 Example 95 IV 0.05 Preparation 86.68 Copolymer 0.1 1.5 6.72 Example 96 IV 5 Preparation 83.28 Copolymer 3.0 2.0 6.72 Example 97 IV 5 Preparation 79.78 Copolymer 5.0 3.5 6.72 Example 98 IV 5 Preparation 68.28 Copolymer 3.0 2.0 6.72 Example 99 IV 20 Preparation 72.68 Copolymer 0.5 0.1 6.72 Example 100 IV 20 Preparation 42.68 Copolymer 0.1 0.5 6.72 Example 101 IV 50 Preparation 88.13 Copolymer 0.1  0.05 6.72 Example 102 V 5 Preparation 87.73 Copolymer 0.5  0.05 6.72 Example 103 V 5 Preparation 79.78 Copolymer 5.0 3.5 6.72 Example 104 V 5 Preparation 74.78 Copolymer 5.0 3.5 6.72 Example 105 V 10 Preparation 73.08 Copolymer 0.1 0.1 6.72 Example 106 V 20 Preparation 71.78 Copolymer 1.0 0.5 6.72 Example 107 V 20 Preparation 86.73 Copolymer 3.0 3.5 6.72 Example 108 VI 0.05 Preparation 84.73 Copolymer 5.0 3.5 6.72 Example 109 VI 0.05 Preparation 87.68 Copolymer 0.5 0.1 6.72 Example 110 VI 5 Preparation 84.28 Copolymer 3.0 1.0 6.72 Example 111 VI 5 Preparation 68.28 Copolymer 3.0 2.0 6.72 Example 112 VI 20 Preparation 61.28 Copolymer 1.0 1.0 6.72 Example 113 VI 30 Preparation 39.73 Copolymer  0.05 3.5 6.72 Example 114 VI 50 Preparation 42.28 Copolymer 0.5 0.5 6.72 Example 115 VI 50 Preparation 38.279 Copolymer 5.0  0.001 6.72 Example 116 VI 50 Comparative 68.28 Copolymer 5.0 — 6.72 Example 16 III 20 Comparative 58.28 Copolymer 5.0 — 6.72 Example 17 III 30 Comparative 58.18 Copolymer 0.1 — 6.72 Example 18 III 35 Comparative 57.78 Copolymer 0.5 — 6.72 Example 19 III 35 Comparative 57.28 Copolymer 1.0 — 6.72 Example 20 III 35 Comparative 55.28 Copolymer 3.0 — 6.72 Example 21 III 35 Comparative 43.18 Copolymer 0.1 — 6.72 Example 22 III 50 Comparative 42.78 Copolymer 0.5 — 6.72 Example 23 III 50 Comparative 42.28 Copolymer 1.0 — 6.72 Example 24 III 50 Comparative 89.73 Copolymer — 3.5 6.72 Example 25 IV 0.05 Comparative 92.23 Copolymer 1.0 — 6.72 Example 26 IV 0.05 Comparative 90.23 Copolymer 3.0 — 6.72 Example 27 IV 0.05 Comparative 88.23 Copolymer 5.0 — 6.72 Example 28 IV 0.05 Comparative 87.78 Copolymer — 0.5 6.72 Example 29 IV 5 Comparative 78.28 Copolymer 10.0  — 6.72 Example 30 IV 5 Comparative 83.28 Copolymer — — 6.72 Example 31 IV 10 Comparative 78.28 Copolymer 5.0 — 6.72 Example 32 IV 10 Comparative 39.78 Copolymer — 3.5 6.72 Example 33 IV 50 Comparative 42.78 Copolymer 0.5 — 6.72 Example 34 IV 50 Comparative 42.28 Copolymer 1.0 — 6.72 Example 35 IV 50 Comparative 40.28 Copolymer 3.0 — 6.72 Example 36 IV 50 Comparative 38.28 Copolymer 5.0 — 6.72 Example 37 IV 50 Comparative 93.23 Copolymer — — 6.72 Example 38 V 0.05 Comparative 93.13 Copolymer 0.1 — 6.72 Example 39 V 0.05 Comparative 92.73 Copolymer 0.5 — 6.72 Example 40 V 0.05 Comparative 92.23 Copolymer 1.0 — 6.72 Example 41 V 0.05 Comparative 90.23 Copolymer 3.0 — 6.72 Example 42 V 0.05 Comparative 88.23 Copolymer 5.0 — 6.72 Example 43 V 0.05 Comparative 84.78 Copolymer — 3.5 6.72 Example 44 V 5 Comparative 69.78 Copolymer — 3.5 6.72 Example 45 V 20 Comparative 63.28 Copolymer — — 6.72 Example 46 V 30 Comparative 88.28 Copolymer — — 6.72 Example 47 VI 5 Comparative 78.28 Copolymer 5.0 — 6.72 Example 48 VI 10 Comparative 58.18 Copolymer 0.1 — 6.72 Example 49 VI 35 Comparative 57.78 Copolymer 0.5 — 6.72 Example 50 VI 35 Comparative 57.28 Copolymer 1.0 — 6.72 Example 51 VI 35 Comparative 55.28 Copolymer 3.0 — 6.72 Example 52 VI 35 Comparative 53.28 Copolymer 5.0 — 6.72 Example 53 VI 35

4. Evaluation of Properties

The properties of the lubricant compositions prepared in Preparation Examples and Comparative Examples were measured as follows. The results are shown in Tables 6 and 7 below.

Friction Coefficient

In the ball-on-disc mode, friction performance was evaluated by sequentially elevating the temperature in increments of 100 from 40 to 120□ at 50 Hz and comparing the average friction coefficients at individual temperatures.

Here, the friction coefficient value decreases with an increase in effectiveness.

Traction Coefficient

The traction coefficient was measured using an MTM instrument made by PCS Instruments. Here, the measurement conditions were fixed at 50N and SRR 50%, and friction and traction were observed depending on changes in temperature. The temperature was varied from 40 to 120□, and the average values were compared.

Wear Resistance

Four steel balls were subjected to friction with the lubricant composition for 60 min under conditions of 20 kg load, 1200 rpm, and 540, the sizes of wear scars were compared, and evaluation was carried out in accordance with ASTM D4172. Here, the wear scar (average wear scar diameter, μm) value decreases with an increase in effectiveness.

Oxidation Stability

Oxidation stability was measured using an RBOT (Rotational Bomb Oxidation Test) meter in accordance with ASTM D2271.

TABLE 6 4 Ball Oxidation SRV Friction MTM Traction Wear stability Coefficient Coefficient (μm) (RBOT, min) Preparation 0.701 0.598 496 610 Example 1 Preparation 0.732 0.569 477 654 Example 2 Preparation 0.734 0.587 432 523 Example 3 Preparation 0.735 0.544 501 320 Example 4 Preparation 0.712 0.523 665 249 Example 5 Preparation 0.288 0.221 142 1580 Example 6 Preparation 0.285 0.200 152 1650 Example 7 Preparation 0.265 0.236 133 1600 Example 8 Preparation 0.264 0.219 121 1480 Example 9 Preparation 0.267 0.211 110 2000 Example 10 Preparation 0.240 0.236 106 2110 Example 11 Preparation 0.736 0.569 511 333 Example 12 Preparation 0.246 0.222 116 2420 Example 13 Preparation 0.239 0.207 123 1840 Example 14 Preparation 0.257 0.217 140 1680 Example 15 Preparation 0.745 0.564 522 285 Example 16 Preparation 0.258 0.213 146 1590 Example 17 Preparation 0.259 0.243 147 1510 Example 18 Preparation 0.754 0.555 536 278 Example 19 Preparation 0.264 0.222 149 1540 Example 20 Preparation 0.768 0.561 555 269 Example 21 Preparation 0.769 0.532 622 298 Example 22 Preparation 0.774 0.512 654 277 Example 23 Preparation 0.744 0.533 635 279 Example 24 Preparation 0.730 0.612 598 311 Example 25 Preparation 0.741 0.633 590 312 Example 26 Preparation 0.745 0.654 455 322 Example 27 Preparation 0.756 0.687 478 388 Example 28 Preparation 0.725 0.698 497 368 Example 29 Preparation 0.76 0.685 518 384 Example 30 Preparation 0.769 0.696 523 368 Example 31 Preparation 0.778 0.641 537 321 Example 32 Preparation 0.792 0.621 556 325 Example 33 Preparation 0.791 0.632 631 387 Example 34 Preparation 0.269 0.219 106 1650 Example 35 Preparation 0.279 0.245 108 1440 Example 36 Preparation 0.793 0.612 623 345 Example 37 Preparation 0.797 0.587 647 388 Example 38 Preparation 0.755 0.555 612 321 Example 39 Preparation 0.702 0.665 678 654 Example 40 Preparation 0.682 0.610 598 523 Example 41 Preparation 0.713 0.587 599 320 Example 42 Preparation 0.715 0.588 587 333 Example 43 Preparation 0.257 0.219 185 1490 Example 44 Preparation 0.259 0.236 168 2110 Example 45 Preparation 0.278 0.217 135 1580 Example 46 Preparation 0.279 0.213 108 1490 Example 47 Preparation 0.284 0.222 154 1480 Example 48 Preparation 0.231 0.247 163 2456 Example 49 Preparation 0.247 0.278 169 2122 Example 50 Preparation 0.264 0.248 185 2020 Example 51 Preparation 0.255 0.256 154 1854 Example 52 Preparation 0.254 0.219 165 1681 Example 53 Preparation 0.678 0.512 655 279 Example 54 Preparation 0.269 0.213 116 1610 Example 55 Preparation 0.278 0.243 123 1440 Example 56 Preparation 0.744 0.587 478 347 Example 57 Preparation 0.623 0.588 676 348 Example 58 Preparation 0.634 0.521 618 384 Example 59 Preparation 0.709 0.569 589 368 Example 60 Preparation 0.745 0.587 599 348 Example 61 Preparation 0.725 0.555 568 384 Example 62 Preparation 0.756 0.548 534 368 Example 63 Preparation 0.284 0.236 147 2410 Example 64 Preparation 0.291 0.245 149 1810 Example 65 Preparation 0.264 0.247 108 1560 Example 66 Preparation 0.284 0.256 110 1540 Example 67 Comparative 0.721 0.589 454 510 Example 1 Comparative 0.759 0.674 505 348 Example 2 Comparative 0.775 0.555 436 258 Example 3 Comparative 0.811 0.588 698 412 Example 4 Comparative 0.766 0.672 664 510 Example 5 Comparative 0.716 0.521 499 285 Example 6 Comparative 0.717 0.569 580 278 Example 7 Comparative 0.726 0.587 590 269 Example 8 Comparative 0.725 0.611 510 465 Example 9 Comparative 0.691 0.587 651 419 Example 10 Comparative 0.711 0.547 587 322 Example 11 Comparative 0.68 0.563 636 249 Example 12 Comparative 0.7 0.587 597 321 Example 13 Comparative 0.716 0.539 498 396 Example 14

TABLE 7 4 Ball Oxidation SRV Friction MTM Traction Wear stability Coefficient Coefficient (μm) (RBOT, min) Preparation 0.291 0.219 121 1660 Example 68 Preparation 0.268 0.209 122 1640 Example 69 Preparation 0.269 0.236 132 1490 Example 70 Preparation 0.264 0.221 159 2020 Example 71 Preparation 0.247 0.200 164 2110 Example 72 Preparation 0.231 0.236 176 2030 Example 73 Preparation 0.255 0.219 157 1650 Example 74 Preparation 0.254 0.211 161 1580 Example 75 Preparation 0.251 0.236 196 1490 Example 76 Preparation 0.260 0.222 186 1910 Example 77 Preparation 0.269 0.207 193 1480 Example 78 Preparation 0.278 0.222 190 1650 Example 79 Preparation 0.279 0.219 176 1680 Example 80 Preparation 0.284 0.245 189 2020 Example 81 Preparation 0.755 0.587 458 249 Example 82 Preparation 0.798 0.639 655 346 Example 83 Preparation 0.768 0.589 636 347 Example 84 Preparation 0.736 0.598 664 258 Example 85 Preparation 0.747 0.569 673 269 Example 86 Preparation 0.231 0.219 152 1790 Example 87 Preparation 0.255 0.211 169 1560 Example 88 Preparation 0.822 0.587 676 287 Example 89 Preparation 0.813 0.544 618 288 Example 90 Preparation 0.279 0.236 147 2110 Example 91 Preparation 0.278 0.219 146 2020 Example 92 Preparation 0.713 0.555 591 412 Example 93 Preparation 0.693 0.548 587 322 Example 94 Preparation 0.704 0.512 541 368 Example 95 Preparation 0.277 0.245 149 2030 Example 96 Preparation 0.284 0.209 198 1650 Example 97 Preparation 0.715 0.555 612 345 Example 98 Preparation 0.269 0.256 110 1910 Example 99 Preparation 0.264 0.219 121 1480 Example 100 Preparation 0.722 0.589 676 610 Example 101 Preparation 0.291 0.236 132 1680 Example 102 Preparation 0.268 0.221 158 1480 Example 103 Preparation 0.713 0.532 580 365 Example 104 Preparation 0.645 0.555 589 285 Example 105 Preparation 0.255 0.236 194 1610 Example 106 Preparation 0.231 0.211 169 1854 Example 107 Preparation 0.758 0.512 578 321 Example 108 Preparation 0.759 0.563 579 325 Example 109 Preparation 0.251 0.207 154 2080 Example 110 Preparation 0.260 0.234 169 2130 Example 111 Preparation 0.261 0.226 226 1780 Example 112 Preparation 0.275 0.217 169 1790 Example 113 Preparation 0.813 0.613 501 415 Example 114 Preparation 0.734 0.580 512 369 Example 115 Preparation 0.784 0.571 523 358 Example 116 Comparative 0.702 0.569 589 299 Example 16 Comparative 0.682 0.564 597 388 Example 17 Comparative 0.726 0.512 478 347 Example 18 Comparative 0.735 0.533 436 321 Example 19 Comparative 0.749 0.523 505 247 Example 20 Comparative 0.748 0.532 518 258 Example 21 Comparative 0.725 0.621 556 401 Example 22 Comparative 0.704 0.633 623 369 Example 23 Comparative 0.779 0.666 655 358 Example 24 Comparative 0.725 0.555 651 269 Example 25 Comparative 0.779 0.563 523 388 Example 26 Comparative 0.77 0.611 498 396 Example 27 Comparative 0.691 0.587 599 348 Example 28 Comparative 0.711 0.588 568 384 Example 29 Comparative 0.716 0.672 647 346 Example 30 Comparative 0.717 0.499 698 347 Example 31 Comparative 0.745 0.623 612 299 Example 32 Comparative 0.711 0.639 673 519 Example 33 Comparative 0.702 0.598 618 654 Example 34 Comparative 0.632 0.569 589 523 Example 35 Comparative 0.612 0.587 597 320 Example 36 Comparative 0.643 0.547 591 333 Example 37 Comparative 0.756 0.610 698 412 Example 38 Comparative 0.758 0.600 678 415 Example 39 Comparative 0.759 0.588 598 369 Example 40 Comparative 0.76 0.541 599 358 Example 41 Comparative 0.769 0.563 587 347 Example 42 Comparative 0.778 0.522 499 321 Example 43 Comparative 0.715 0.543 590 399 Example 44 Comparative 0.749 0.555 587 321 Example 45 Comparative 0.646 0.569 523 278 Example 46 Comparative 0.76 0.611 624 387 Example 47 Comparative 0.822 0.601 444 412 Example 48 Comparative 0.769 0.587 584 345 Example 49 Comparative 0.778 0.588 562 346 Example 50 Comparative 0.792 0.541 532 347 Example 51 Comparative 0.791 0.513 521 258 Example 52 Comparative 0.793 0.555 511 269 Example 53

As is apparent from Tables 6 and 7, the lubricant compositions including the liquid ethylene alphaolefin copolymer, the phosphorothioate compound and the phosphonium phosphate within the amount ranges of the present invention were significantly reduced in wear scar and friction coefficient compared to the lubricant compositions of Comparative Examples, and also exhibited superior oxidation stability. Therefore, it is concluded that the lubricant composition of the present invention is improved from the aspects of friction characteristics and stability and thus is suitable for use in hydraulic oil.

Although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

What is claimed is:
 1. A lubricant composition, comprising: a base oil, a liquid olefin copolymer, a phosphorothioate compound, and phosphonium phosphate.
 2. The lubricant composition of claim 1, wherein the liquid olefin copolymer is prepared by copolymerizing ethylene and alphaolefin using a single-site catalyst system.
 3. The lubricant composition of claim 1, wherein the phosphorothioate compound is at least one selected from the group consisting of monophosphorothioate, diphosphorothioate, triphosphorothioate, methylphosphorothioate, ethylphosphorothioate, and sulfonylphosphorothioate.
 4. The lubricant composition of claim 1, wherein the phosphonium phosphate has a structure of Chemical Formula 7 below.


5. The lubricant composition of claim 2, wherein the single-site catalyst system includes a metallocene catalyst, an organometallic compound and an ionic compound.
 6. The lubricant composition of claim 1, wherein the liquid olefin copolymer has a coefficient of thermal expansion of 3.0 to 4.0.
 7. The lubricant composition of claim 1, wherein the liquid olefin copolymer has a bromine number of 0.1 or less.
 8. The lubricant composition of claim 1, wherein the phosphorothioate compound is included in an amount of 0.1 to 5.0 wt % in the lubricant composition.
 9. The lubricant composition of claim 1, wherein the liquid olefin copolymer is included in an amount of 0.5 to 30 wt % in the lubricant composition.
 10. The lubricant composition of claim 1, wherein the base oil is at least one selected from the group consisting of mineral oil, polyalphaolefin (PAO), and ester.
 11. The lubricant composition of claim 1, further comprising an additive selected from the group consisting of an antioxidant, a metal cleaner, an anticorrosive agent, a foam inhibitor, a pour-point depressant, a viscosity modifier, a wear-resistant agent, and combinations thereof.
 12. The lubricant composition of claim 1, wherein the lubricant composition has an SRV friction coefficient of 0.1 to 0.35.
 13. The lubricant composition of claim 1, wherein the lubricant composition has a traction coefficient of 0.15 to 0.3.
 14. The lubricant composition of claim 1, wherein the lubricant composition endures 1000 min or more in an oxidation stability evaluation (RBOT, ASTM D2271).
 15. The lubricant composition of claim 1, wherein the lubricant composition is used as hydraulic oil. 